Gas, tires, oil.

I’ve been wanting to do a couple led projects, but the lack of cheap leds has been holding me back. Last year, over at the Make blog, someone mentioned using led christmas lights as a source for leds. We hit some day after christmas sales and got three packs of white and one of colored led lights. The whites are going to be for interior lights for my camper trailer, but here I’m going to show how to convert a regular flashlight to led using red leds. I wanted red so that would have flashlight for camping that wouldn’t wreck my night vision (astronomers, the military, wildlife photographer all use red filters on their lights because they preserve your night vision). I was just going to use some sort of red filter, but found this idea on an amature astronomy website. The colored lights used 70 2V leds (what it specified as replacement bulbs anyway) in series (one light goes out, they all go out). 2V seemed like an odd voltage, but they were run on AC, so maybe that’s RMS. I found that they work nicely with 2 dry cells (~3 V).

The leds are in holders that plug in to sockets, you just need to straighten out the legs to remove them. Those sockets may be nice for other led projects. I happened to have a burned out flashlight bulb hanging around. I broke the glass with a pair of pliers.

Now I had to find out which of the filament holders was ground (negative), I used a multimeter. The wikipedia page on leds is a nice reference for determining the polarity of leds, but basically the negative lead is shorter and base has a flat on it. Next I trimmed leads on the leds (has to be short enough not to hit flashlight lens) and soldered them (in parallel) to the filament holders of the flashlight bulb.

They also have to fit through the hole in the flashlight reflector, 2 barely fit, but with some trimming 3 might go.

The AA batteries should run forever with these leds, and while its not terribly bright, its perfect for what I want it for: finding a keyhole or navigating inside the camper without losing my night vision (the camera makes the light look much more yellow than it is).